In the field of radio communication, a MIMO (Multiple-Input and Multiple-Output) transmission scheme has been utilized, which realizes an improvement in the speed and quality of signal transmission by executing transmission and reception using multiple antennas on each of a radio transmission station side and a radio reception station side.
In order to further improve signal transmission speed and further reduce interference, a massive-MIMO transmission scheme has been considered, which uses a large number of antenna elements (e.g., 100 elements or more) in a high frequency band (e.g., 10 GHz or more) that enables antenna miniaturization and in which a wide bandwidth can be secured (e.g., Patent Document 1). For example, in a mobile communication system supporting UMTS (Universal Mobile Telecommunications System) LTE-A onward, the use of a Massive-MIMO transmission scheme is under consideration.
In massive-MIMO, advanced beamforming (BF) can be implemented that uses a greater number of antenna elements in comparison to conventional MIMO. Beamforming is a technology that involves controlling the directivity and shape of a beam (e.g., a transmission beam corresponding to a transmitting antenna, a reception beam corresponding to a receiving antenna) by controlling antenna elements. With MIMO, the phase and amplitude can be controlled for each antenna element, and therefore, the flexibility of beam control increases with an increase in the number of antenna elements that are used.